1. Field of the Invention
This invention pertains to ceramics and more specifically to a method of mixing ceramic powders.
2. Description of the Prior Art
The strength of ceramics, as well as other physical, mechanical and dielectric properties, are controlled by the impurities and uniformity of the microstructure. Since ceramics are usually composed of several different compounds, it is necessary to thoroughly blend these powders together prior to sintering; this is accomplished by ball milling or other grinding techniques. Unfortunately, not only are impurities introduced into the starting powder which are detrimental to the sintered part, but also agglomerates form which preclude uniform mixing.
In copending application Ser. No. 558,225 filed Dec. 5, 1983, the inventors Walter et al teach another method for improving the strength of silicon nitride. That method comprises placing the silicon nitride object in a furnace in a gaseous atmosphere and subjecting the object to a hot isotatic pressing (HIP'ing) process at a temperature ranging from about 1600.degree. to 1700.degree. C.
Despite these improvements in the strength of ceramics, significant improvements are yet needed in order to make ceramics a more viable structural material.
Further, it should be known that Alan Bleier, in May 1983 Communications of the American Ceramic Society, authored an article entitled "Fundamentals of Preparing Suspensions of Silicon and Related Ceramic Powders". This article was directed at the use of specific kinds of dispersion liquids and recorded those which had good dispersion characteristics.
John S. Haggerty and W. Roger Cannon authored a paper entitled "Sinterable Powders from Laser Driven Reations, Third Annual Report", the report period being from July 1, 1979 through June 30, 1980. This report was prepared at the Massachusetts Institute of Technology for the U.S. Department of Defense. In that report, the authors discussed the use of dispersing liquids similar to those of Bleier above, and also at page 58 indicated that ultrasonic agitation could be used to enhance wetting, dispersion, and fragmentation of agglomerates.